I just tried an A7C at a Sony store, coupled with their 35/1.8. I was impressed with how compact it is, and I love the rangefinder-like EVF position: it allows for a shallow eye rest that helps to keep the camera's dimensions compact, as a right-eyed shooter's nose won't be touching any part of the camera when looking through its EVF. The A7C does have a boring design, just like every other Sony camera, and worse it lacks a front command wheel. Nikon engineers could come up with a much better-looking, and way more functional body than the Sony A7C just by taking some inspiration from the old S rangefinder line (they all had a front "command wheel" even back then!). Actually, I am sure they already have something akin on their drawing boards, if not in prototype form already. I would buy one if they make it as handsome as the Zfc.
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As to the OP, I don’t really want anything more compact than the fc. If i am going more compact then I’ll use my phone which competes with the fc and 28mm for IQ. I would however love a apsc stacked sensor body that I can put my 100-400 on, with my Z9 taking the 800mm.